问题 填空题

遗传物质主要存在于______中.染色体的主要成分是______和______,其中后者就是通常所说的______(英文简写)

答案

染色体是细胞核中容易被碱性染料染成深色的物质,染色体是由DNA(脱氧核糖核酸 )和蛋白质两种物质组成;DNA是遗传信息的载体,是主要的遗传物质.主要存在于细胞核中,DNA分子为双螺旋结构,像螺旋形的梯子;DNA上决定生物性状的小单位,叫基因.

故答案为:细胞核  蛋白质  脱氧核糖核酸  DNA

阅读理解

阅读理解。裉据短文内容判断正(T) 误(F) 。

     These two letters appeared in a newspaper. Both writers have their own ideas on zoos.

                                                                 Zoos Do a Good Job

    It is good to keep animals in zoos. I know a lot of people think it is wrong to keep animals in zoos.

 However, I believe that zoos have many good points.

    Firstly, zoos are places for people to see different animals from all over the world. Without the zoos,

 most people would never see a real bear or tiger.

       Secondly, zoos look after the animals very well. The animals are always given food and cleaned

 regularly (定期的). In the wild, it is not always possible for an animal to find food, so sometimes it goes

  hungry. But animals kept in zoos never go hungry.

     Thirdly, zoos protect the animals they look after. They offer them safe places to live in. In the wild,

 some kinds of animals are in danger of becoming extinct (灭绝的). But zoos give these animals a chance

 to live. Without zoos. There would be fewer kinds of animals in the world.

                                                                                                                          Maria Smith

                                                                      Zoos are Unnatural

     In Maria's letter, she says that zoos are good for animals. I am afraid that zoos are not good for

 animals, they are only good for people.

      It is unnatural and unfair to keep wild animals in cages. Most animals are kept in cages that are too

 small for them. In the wild, these animals would travel freely In zoos. They can't do this. This is why the

 bears and tigers always look so sad.

        Most cages are not very clean, either. It is true that zoos give the animals food regularly, but this is

 not natural. Wild animals are used to looking for their own food. We should treat animals in the same

 way that we treat other people with respect.

       Would anyone be happy if you don't let them go outside his home? Would Maria like to have lots of

 people stand out side her flat looking at her? No, she wouldn't. And animals don't like it, either.

                                                                                                                                Philip Black

1. Maria and Philip have quite different ideas on keeping animals in zoos.

2. In Maria's opinion, a real bear or tiger can only be seen in zoos.

3. Maria thinks that animals live better in zoos than in the wild.

4. According to Philip, if cages are big and clean enough, tigers and bears will look happy.

5. Maria and Philip both agree that zoos are good for people.

单项选择题